The goals of Core D are to provide electron microscopic ultrastructure support to Projects 1, 2, 3 and 4[unreadable] We expect that a structural analysis of protein disposition within the calcium release units (CRUs) and of the[unreadable] factors that affect assembly of complete CRUs will significantly enhance to our understanding of their function[unreadable] and the dysfunction caused by MH/CCD mutations in RyR1.[unreadable] A1. To determine the effect of MH/CCD RyR1 mutations on the ultrastructure of affected skeletal[unreadable] muscle. We will define any ultrastructural abnormalities caused my MH/CCD mutations, paying particular[unreadable] attention to triadic RyR-DHPR relationships and calsequestrin (Supporting Projects 1, 2, 3, 4 and in[unreadable] collaboration with Cores B and C).[unreadable] A2. To detect evidence for RyR conformational changes and for structural changes in DHPR/RyR[unreadable] conformational coupling by assessing alterations in DHPR tetrad parameters resulting from MH/CCD[unreadable] mutations in RyR1. We will determine the relative effectiveness of mouse and human MH/CCD RyRs to[unreadable] coordinate tetrad formation and to determine if these mutations alter intra or inter tetrad spacing. (Supporting[unreadable] 1, and 2 in collaboration with Cores B and C).[unreadable] A3. To define the structural relationship between mitochondria and the SR during development/aging[unreadable] and determine if there are differences in this relationship between wt and MH/CCD mice. Our[unreadable] preliminary data indicate that mitochondria gradually acquire very specific locations relative to the triads[unreadable] during postnatal development. In addition we will determine the structural integrity of both the SR and the[unreadable] mitochondria in homozygous and heterozygous MH mice. (Supporting Projects 1, 3, and 4).[unreadable] A4. To detect CRUs in mature dendritic cells isolated from control and homozygous MH/CCD muscle[unreadable] and to define their structure. We will define the ultrastructure of sites where RyR1 and CaV1.3 are[unreadable] co-localized in dendritic cells (DC) and detect any variations introduced by the MH/CCD mutations[unreadable] (Supporting project 2)